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7th International Conference on Modeling and Diagnostics for Advanced Engine Systems, COMODIA 2008

作者： Chen, Gen Huang, Zuohua Chen, Chaoyang Miao, Haiyan Wang, Xibin Jiang, Deming State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an 710049 China

The premixed flames of DME-hydrogen-air premixed mixture were studied by the outwardly expanding flame and schlieren photography. The influences from equivalence ratio, hydrogen addition and initial pressure on the flame speed and combustion characteristics are analyzed. The results show that the flame speed, the laminar burning velocity and the mass burning rate increase with the increase of hydrogen addition. Increasing the ratio of hydrogen to DME will shorten the combustion duration. In the case of small hydrogen addition, the Markstein length decreases with the increase of equivalence ratio, and this reveals that lean mixture has better flame front stability than of rich mixture. In the case of large hydrogen addition, the Markstein length increases with the increase of equivalence ratio, and this indicates that rich mixture has better flame front stability than that of lean mixture. The initial pressure has larger influence on the combustion pressure than that from hydrogen addition. The flame development duration decreases with the increase of hydrogen addition and/or with the increase of equivalence ratio. Addition of hydrogen into DME can improve the ignitability of the mixtures and fasten the combustion. Copyright © 2008 by the Japan Society of Mechanical Engineers.

关键词： Hydrogen

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Characteristics of HCN removal using cao at high temperatures

Characteristics of HCN removal using cao at high temperature...

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作者： Houzhang, Tan Xuebin, Wang Congling, Wang Tongmo, Xu State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniVersity Shaanxi 710049 China

Experimental investigation on the removal of hydrogen cyanide (HCN) using calcium oxide (CaO) was carried out in a fixed bed reactor at temperature ranging from 300 to 1173 K, and the original HCN was produced during the pyrolysis of pyridine. Effects of temperature, volume space velocity, and initial HCN concentration on HCN removal were discussed. The results of temperature-programmed experiments show that temperature is the main factor affecting HCN removal. With the formation of CO, HCN starts to decrease from 473 K, and remains unchanged from 673 to 873 K. At 873 K, there is a further decrease in HCN without CO formation, and when temperature is higher than 1023 K, HCN is removed completely. In the isothermal experiments, CaCN2 was detected at 723 K, but at higher temperatures of 923 and 1123 K, there was no CaCN2 in the solid residues, and the nitrogen in the removed HCN was equal to that in the formed N2. This indicates that at a lower temperature CaO is consumed to remove HCN, CaO + 2HCN f CaCN2 + CO + H2;but at a higher temperature, CaO acts as a catalyst for HCN removal, 2CiHj + 2HCN f N2 + (j + 1 - k)H2 + 2Ci+1Hk. The investigation on the removal efficiency shows that there is a critical temperature and a critical volume space velocity at which the HCN removal efficiency is able to reach up to 100%. © 2009 American Chemical Society.

关键词： Temperature

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Numerical investigations on cluster characteristics in the supercritical water circulating fluidized bed riser

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Particuology 2024年第11期94卷 281-293页

作者： Kenan Xi Runqing Li Xiazhi Li Mei Li Xiudong Xu Yu Zhang Hao Wang Youjun Lu Northwest Institute of Nuclear Technology Xi'an710024China State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong UniversityXi'an710049China Xi'an Institute of Applied Optics Xi'an710065China

There are currently no reports about clusters in the supercritical water circulating fluidized bed(SCWCFB).Simulations were conducted to investigate the numbers,diameters,aspect ratios,circularity,and orientation angles of cluster in the riser of SCWCFB via two-fluid model across different flow velocities,solid circulation rates,pressures,and *** results show that cluster numbers are mainly between 10 and 80 per *** are more at the bottom but less at the top,and more near the wall but less at the *** diameters are mainly between 0.2 and 0.5 times the bed *** are large at the bottom but small at the top,and large at the center but small near the *** aspect ratios are mainly between 0 and 1,indicating that most clusters have shorter width than their ***-like clusters are more likely to appear near the walls,and clusters at the center of the riser are more likely to be *** circularity is mainly between 0.2 and 0.4,suggesting that the shapes of clusters are far from the *** absolute values of cluster orientation angles are mainly between 75°and 90°,indicating that most clusters move in the vertical *** fluid velocities may facilitate cluster coalescence.

关键词： Supercritical water Circulating fluidized bed Cluster Two-fluid model Riser

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Effect of partially premixed and hydrogen addition on lean burn natural gas direct injection combustion 7

Effect of partially premixed and hydrogen addition on lean b...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Wang, J.H. Huang, Z.H. Zheng, J.J. Miao, H.Y. State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

Effect of partially premixed and hydrogen addition on lean burn natural gas direct injection combustion was studied experimentally using a constant volume vessel. Flame propagating photos and pressure derived combustion parameters were analyzed at different premixed ratios (from 0% to 80%) and hydrogen fractions (from 0% to 40%) at overall equivalence ratio of 0.6 and 0.8, respectively. The results showed that the flame kernel was concentrated to the spark position with the increase of premixed ratio and/or hydrogen fraction. The flame propagating speed was increased with hydrogen addition to natural gas. The stable spark ignition of lean burn natural gas was realized with the combination of partially premixed direct injection combustion and hydrogen addition. Both the initial and main combustion durations were increased with the increase of premixed ratio, while they showed the decreasing trend with hydrogen addition to natural gas. Partially premixed direct injection combustion combing with hydrogen addition can achieve the stable spark ignition and fast combustion rate at the lean mixture condition. © 2009 Combustion Institute. All rights reserved.

关键词： Natural gas

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Effects of hydrogen addition on cellular instabilities of the spherically expanding propane flames 7

Effects of hydrogen addition on cellular instabilities of th...

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7th Asia-Pacific Conference on Combustion, ASPACC 2009

作者： Tang, C.L. Huang, Z.H. Wang, J.H. Zheng, J.J. State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

An experimental study on the effects of hydrogen addition on the instabilities of spherically expanding propane-air flames was conducted in a constant volume combustion vessel over a wide range of mixture compositions and initial temperatures and pressures. The measured laminar burning velocities were compared with those of the calculated one dimensional freely propagating flames, using a recently developed detailed kinetic mechanism, and the agreement was excellent. The schlieren images show that for the fuel lean conditions, hydrogen addition increases the hydrodynamic instability due to the decreased flame thickness and increases diffusional-thermal instability due to the decreased Lewis number, while for the fuel rich conditions, the flame front is initially destabilized and later stabilized with the increase of hydrogen fraction as the results of the competing effects of hydrodynamic and diffusional-thermal instabilities © 2009 Combustion Institute. All rights reserved.

关键词： Propane

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Specific Heat Ratio of High Methane Fraction Natural Gas/Air in Confined Vessel

Specific Heat Ratio of High Methane Fraction Natural Gas/Air...

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SAE 2015 World Congress and Exhibition

作者： Tang, Chenglong Si, Zhanbo Zhang, Shuang Huang, Zuohua Pan, Shiyi Wang, Jinhua Gong, Jing Xi'An Jiaotong University State Key Laboratory of Multiphase Flow in Power Engineering Xi'an710049 China

The specific heat ratio used in heat release calculation plays an important role and the mass fraction burned is also a crucial parameter in thermodynamics analysis for engine combustion. A research of high methane fraction natural gas was investigated in a constant volume combustion vessel at different initial conditions. Results show that with the increase of the initial pressure, the specific heat ratio is decreased, and the time of the mixture burned up is postponed, while the peak heat release ratio is increased. With the increase of the methane fraction, the parameters have the opposite behavior. With the increase of the initial temperature, the specific heat ratio is decreased, and the time when the mixture is burned up is accelerated, and the peak heat release ratio has no obviously difference. With the increase of the dilution ratio or the CO2/N2 ratio, the specific heat ratio is decreased, and the peak heat release heat ratio is decreased. Meanwhile, the time of mixture burned up is postponed with the increase of dilute ratio or CO2/ N2 ratio. Copyright © 2015 SAE International.

关键词： Specific heat

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A Least-Squares Solution to Nonlinear Steady-state Multi-Dimensional IHCP

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Journal of Thermal Science 1996年第1期5卷 39-41页

作者： Bai Bofeng Guo Liejin Chen Xuejun (state key Lab of multiphase flow in power engineering,Xi’an Jiao Tong University,Xi’an 710049,China) State Key Lab of Multiphase Flow in Power Engineering Xi’an Jiao Tong University Xi’an China

In this paper,the least-squares method is used to solve the Inverse Heat Conduction Problem(IHCP)to determine the space-wise variation of the unknown boundary condition on the inner surface of a helically coiled tube with fluid flow inside,electrical heating and insulation *** sensitivity coefficient is analyzed to give a rational distribution of the thermocouples. The results demonstrate that the method effectively extracts information about the unknown boundary condition for the heat conduction problem from the experimental measurements. The results also show that the least-squares method converges very quickly.

关键词： helically coiled tube least-squares method IHCP.

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Large eddy simulation on the respective roles of integral length scale and turbulence intensity on turbulent premixed combustion 12

Large eddy simulation on the respective roles of integral le...

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12th Asia-Pacific Conference on Combustion, ASPACC 2019

作者： Shilong, Guo Meng, Zhang Jinhua, Wang Xutao, Wei Zuohua, Huang State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

The effects of integral length scale () and turbulence intensity (? ) on premixed combustion are studied using large eddy simulation. Three groups of lean CH4/air flames are carried out using the thickened flame model combined with a two-step reduced chemical mechanism. Two groups vary at constant ? and the other group increases ? from low to high while keeping unchanged. One of the cases is validated to available experimental data, showing good agreement for the flame-brush structure. The numerical results show that the increase in or ? leads to a decrease in flame-brush height and an increase in flame-brush thickness and volume. The turbulent flame speed () will be enhanced by these two factors within the scope of our study. All the flame-brush structure data, including height, thickness, volume and area, and also collapse onto a single line when the turbulent Reynolds number is used as abscissa. The probability density function distributions of filtered thickened flame front curvature show that will be increased by and ? through increasing the amount of large-scale and small-scale wrinkling structures respectively. © Asia-Pacific Conference on Combustion, ASPACC *** right reserved.

关键词： Large eddy simulation

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Kinetics of oxygen bubble growth in water decomposition

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Wuli Xuebao/Acta Physica Sinica 2025年第10期74卷

作者： Nie, Tengfei Xu, Qiang Luo, Xinyi Hong, Aoyue Cao, Zeshui Guo, Liejin State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Xi’an710049 China

In order to enhance the efficiency of large-scale water decomposition, it is important to understand the oxygen bubble evolution on the electrode surface. In this work, a numerical model for the growth of oxygen bubbles on the electrode surface is proposed based on the dissolved oxygen flux at the bubble boundary, and the mechanisms of the reaction area and current during the bubble growth are investigated. The results show that the bubble diameters calculated from the oxygen flux at the bubble boundary are in good agreement with the diameters of the bubbles growing in the control phase of the chemical reaction. As the reaction region increases, the transition time from the diffusion-controlled stage to the chemical reaction-controlled stage becomes longer during the bubble growth. The concentration maximum value on the microelectrode surface is significantly higher than that on the large electrode surface, which leads to a steeper concentration gradient between the microelectrode surface and the bubble surface. As the current increases, the bubble growth rate increases and the time coefficient decreases faster. The bubble diameter at a current of 0.06 mA accords well with the bubble diameter at a current of 0.1 mA in the photoelectrochemical water splitting experiments. This is because the scattering of light by the growing bubbles leads to a decrease in the current density at the bottom of the bubble.(Figure Presented) © 2025 Chinese Physical Society.

关键词： Pyrolysis

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Evaluation of droplet drag force model on spray and atomization behaviours of R134a flashing spray 14

Evaluation of droplet drag force model on spray and atomizat...

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14th International Conference on Liquid Atomization and Spray Systems, ICLASS 2018

作者： Zhou, Zhi-Fu Lu, Guan-Yu Zhang, Lu Chen, Bin State Key Laboratory of Multiphase Flow in Power Engineering Xi'an Jiaotong University Xi'an710049 China

Flashing spray is of great importance in a variety of engineering fields, which occurs as the pressurized liquid is released into a low-pressure environment below its saturation pressure. This paper conducts a systematically numerical study on the spray and thermal characteristics of R134a flashing spray with high volatility and low saturation temperature, using a modified sprayFoam solver in the open source tool OpenFOAM-2.4.0. key physics involved in the complex process, including droplet flash boiling, evaporation, droplet transport, breakup, heat transfer and interaction between droplet and gas phases are taken into consideration. The emphasis is put on the droplet drag force model and nozzle diameter on flashing spray including spray morphology, droplet diameter, velocity and temperature. The result indicates that most of the drag force models have little effect on droplet diameter, velocity and temperature distributions in flashing spray, except the Khan-Richardson (K-R) model. The K-R model predicts lower temperature, higher velocity and larger size of droplet, compared to other models. The nozzle diameter greatly affects R134a spray morphology and tip penetration, that smaller diameter contributes to a larger radial expansion at the near nozzle region while leading to a much smaller penetration distance. This research give a useful guidance that how people choose the appropriate drag force model for simulation of flashing spray. © 2018 Solar Turbines Incorporated.

关键词： Morphology

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